Eye image imaging device

ABSTRACT

An eye image taking device comprises: an imaging unit for taking an eye of a user as an eye image; a focusing degree calculating unit for calculating the magnitude of high-frequency components from the eye image; a threshold setting unit for setting a focusing threshold intrinsic to an authorized user; and a focus deciding unit for deciding a focus by comparing the magnitude of the high-frequency components and the focusing threshold, so that the optimum focusing threshold is set for the authorized user.

TECHNICAL FIELD

The present invention relates to an eye image taking device and, moreparticularly, to an eye image taking device which can be installed in amobile terminal device.

BACKGROUND ART

Generally, the iris authentication identifies a person by illuminatingthe eye of a user or its circumference with a near infrared ray or thelike, by taking the eye image and the circumference image (as will begenerally called the “eye image”) with a camera, by extracting the irisinformation from the eye image obtained, and by comparing the irisinformation with the iris information which has already been registeredin the iris information database. The eye image taking device to be usedhas to take the eye image highly precisely for extracting the irisinformation of the user precisely. Thus, there has been proposed an eyeimage taking device, which utilizes the automatic focusing technique todetect the eye position from the taken image of the entire face and totake the eye image of a desired size by zooming up that eye with a zoomlens.

In this automatic focusing technique, the control is made by making useof the fact that many high-frequency components are contained in imagesignals if an object is focused (as will be called the “focusing”) sothat the contour image is clearly taken, by integrating thehigh-frequency components in the image signals while varying the lensposition, and by searching the lens position, at which the integratedvalue is the maximum. In order to search the lens position promptly,moreover, there is generally adopted (as referred to JP-A-2000-131598,for example) the so-called “hill-climbing method”, in which the lensposition is gradually varied in the direction for the high-frequencycomponents to increase.

In recent years, on the other hand, as the accounts settling system orthe like using a mobile terminal device such as a mobile telephonespreads, it has been tried to install the iris authenticating functionof a high personal authentication reliability in the mobile terminaldevice. However, the eye image taking device needs a drive system fordriving the lens and has a difficulty in reducing the size and weight ofthe optical system. It has, therefore, been extremely difficult toinstall the eye image taking device having the automatic focusingmechanism in the mobile terminal device such as the mobile telephone.For these reasons, a practical eye image taking device for the mobileterminal device can be proposed by installing a small, light andinexpensive camera using a fixed focus lens, by deciding the focusingdegree with the magnitude of the high-frequency components contained inthe image signals, and by guiding the imaging distance so that themagnitude of the high-frequency components may be larger than apredetermined threshold value.

However, personal differences are large not only in the pattern of aniris and the shapes of the individual portions such as eyelashes oreyelids but also in the magnitude of the high-frequency componentscontained in the eye image signals. Therefore, the method for guidingthe imaging distance so that the magnitude of the high-frequencycomponents may become larger than the predetermined threshold value hasa problem that the stable focus decision cannot be attained dependingupon the shapes of the individual portions of the eye of the user. Thisproblem is exemplified such that some user may fetch the eye image outof focus or can neither attain the focus decision nor fetch the eyeimage.

The present invention contemplates to solve the problems thus fardescribed and has an object to provide an eye image taking device, whichcan make a stable focus decision irrespective of the shapes of theindividual portions of the eye of a user by using the small, light andinexpensive fixed focus lens and which can be installed in a mobileterminal device.

DISCLOSURE OF THE INVENTION

According to the invention, there is provided an eye image taking devicecomprising: an imaging unit for taking an eye image of a user; afocusing degree calculating unit for calculating a focusing degree fromthe eye image taken at the imaging unit; a threshold setting unit forsetting a focusing threshold intrinsic to an authorized user; and afocus deciding unit for deciding a focus by comparing the focusingdegree and the focusing threshold, wherein the threshold setting unitsets the focusing threshold on the basis of the eye image of theauthorized user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 1 of the invention.

FIG. 2 is a diagram schematically showing relations between a focusingdegree and an imaging distance for different users.

FIG. 3 is a flow chart showing an operating procedure at a focusingthreshold setting time in Embodiment 1 of the invention.

FIG. 4 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 2 of the invention.

FIG. 5 is a diagram showing relations of the magnification of an imageto be taken and an iris.diameter to an imaging distance.

FIG. 6 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 3 of the invention.

FIG. 7 is a diagram schematically showing relations between an irisdiameter and a focusing degree for different users.

FIG. 8 is a flow chart showing an iris image taking procedure at an irisauthenticating time in Embodiment 3 of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Eye image taking devices according to embodiments of the invention willbe described with reference to the accompanying drawings.

EMBODIMENT 1

FIG. 1 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 1 of the invention. Eye image takingdevice 100 in Embodiment 1 is provided with: imaging unit 120 for takingan eye image of the user; focusing degree calculating unit 130 forcalculating the magnitude of a high-frequency component contained in theeye image, as a focusing degree; threshold setting unit 150 for settinga focusing threshold intrinsic to an authorized user; focus decidingunit 140 for deciding the focus by comparing the focusing degree and thefocusing threshold; and an illumination unit (although not shown) forilluminating the eye of the user and its circumference by irradiating anear infrared ray in a quantity suited for the eye image acquisition.

Imaging unit 120 includes lens 121, visible light cut filter 122,imaging element 123, image signal processing portion 124 and guidemirror 125. In Embodiment 1, a fixed focus lens is used as lens 121 toreduce the size, weight and cost of the optical system. Guide mirror 125guides the eye of the user to a correct imaging position when the userreflects his or her eye on guide mirror 125. The eye of the user istaken on imaging element 123 through lens 121 and visible light cutfilter 122. Image signal processing portion 124 extracts image signalcomponents from the output signals of imaging element 123 and subjectsthe image signal components as the image signals for gain adjustments toa necessary processing. Image signal processing portion 124 outputs theprocessed image signals as the eye image signals of the user.

Focusing degree calculating unit 130 includes filter portion 131 andintegration portion 132. Filter portion 131 extracts signals ofhigh-frequency components having a predetermined frequency band suitedfor the focusing decision, from the image signals outputted by imagesignal processing portion 124, and outputs the extracted high-frequencycomponent signals to integration portion 132. Integration portion 132integrates the square value or absolute value of the high-frequencycomponents obtained through filter portion 131, within the area of onescreen (or one frame), and outputs the integrated value as the magnitudeof the high-frequency components contained in the eye image. Themagnitude of the high-frequency components outputted from integrationportion 132 and contained in the eye image will be called “focusingdegree F”.

Focus deciding unit 140 performs the decision of focus by comparingfocusing degree F with predetermined focusing threshold Fth by a method,as will be described hereinafter. Thus, the focus deciding outputobtained as the output of focus deciding unit 140 and the eye imageoutput or the output of image signal processing portion 124 are inputtedto the iris authenticating device (although not shown) so that the irisauthentication is made by using the eye image signals which have beendecided as the focus.

Threshold setting unit 150 sets focusing threshold Fth in the followingmanner for the authorized user of a mobile terminal device having eyeimage taking device 100 of Embodiment 1 of the invention installedtherein, such as the terminal use contractor or the terminal owner. Whenthe authorized user registers the iris information, eye images are takenat first at varied distances between eye image taking device 100 and theeye thereby to obtain a plurality of eye images corresponding todifferent imaging distances X, and focusing degrees F are determined forthe individual eye images. Threshold setting unit 150 determines maximumFmax from plural focusing degrees F thus obtained, and determinesfocusing threshold Fth by multiplying maximum Fmax by a predeterminedcoefficient, as will be described hereinafter. In case the authorizeduser changes with transfers or the like, focusing threshold Fth has tobe reset when the new authorized user makes a registration of the irisinformation again in the iris authenticating device.

Here will be described the reason why focusing threshold Fth is set forthe authorized user. FIG. 2 is a diagram schematically showing relationsbetween imaging distance X for different users and focusing degree F.Letters A, B and C designate the relations among three different users.In Embodiment 1, the fixed focus lens is used as lens 121. Therefore,imaging distance Xf, at which focusing degree F takes the maximum, isdetermined by the focal distance (i.e., the distance of just focus) ofthe fixed focus lens and is common among the users. However, therelations between focusing degree F and imaging distance X are differentamong individuals, as shown in FIG. 2. This is partly because the irispatterns are different among individuals so that the high-frequencycomponents contained in the eye images are different among individualsand partly because the high-frequency components are influenced byportions other than the iris, such as eyelashes or eyelids.

In order to acquire the eye image, which is focused for each authorizeduser of each eye image taking device, therefore, maximum Fmax of thefocusing degree intrinsic to each user has to be determined to take theimage at distance Xf, at which focusing degree F is Fmax. In thepractical use, however, it is hard to take the eye image at thatdistance Xf for maximum focusing degree F. It is, therefore, practicalto authenticate the eye image, which has been focused for a practicallytrouble-free iris authentication although focusing degree F has failedto take the maximum, by assuming that the eye image is focused.

FIG. 2 shows this range of imaging distance X as focal range Xw. If thefocusing threshold is set at the value indicated by Fth in FIG. 2, it isproper as the focusing threshold for user A to authenticate the eyeimage, for which focusing degree F exceeds focusing threshold Fth, i.e.,the eye image which is within focal range Xw. For user B, on thecontrary, an eye image, as cannot be authenticated, may be taken as theeye image which can be authenticated. For user C, on the other hand, thefocus decision cannot be obtained. This makes it necessary to setintrinsic focusing threshold Fth optimum for the authorized user. Bythus determining focusing threshold Fth, it is possible to attain aneffect to lower the authentication factor (or another accepting factor)of the unauthorized user (i.e., users B and C shown in FIG. 2).

Even if the users are different, as shown in FIG. 2, the relationsbetween focusing degree F and imaging distance X present generallysimilar shapes. So far as focusing degree F is within the range frommaximum Fmax of the focusing degree to a value smaller at apredetermined ratio, imaging distance X may be within focal range Xw.Therefore, focusing threshold Fth can be determined by multiplyingmaximum Fmax by a predetermined coefficient. In this embodiment, it isassumed that the coefficient is set at 0.8, namely, that the eye imagefalls within the focal range if focusing degree F is 80% or more ofFmax. If the coefficient to multiply maximum Fmax becomes larger, a morefocused satisfactory eye image can be obtained, but the focusing rangeis narrowed to make it hard to obtain the focus deciding result. Thus,the value of the coefficient is desired to be suitably set according tothe optical characteristics of imaging unit 120 or the characteristicsof the iris authenticating device to be connected, and the using purposeof the iris authenticating device.

Here will be described a procedure for determining focusing thresholdFth. FIG. 3 is a flow chart showing an operating procedure at a focusingthreshold setting time in Embodiment 1 of the invention.

First of all, a message to start the focusing threshold setting isoutputted (at S11). At this focusing threshold setting time, plural eyeimages of different imaging distances are needed. The message to beoutputted is “Bring Camera Slowly toward Eye from Arm-ExtendedPosition.” This message may be either displayed by using a display unitsuch as a liquid crystal display panel attached to the mobile terminaldevice or outputted as a speech through an accessory speaker.

Next, the eye image of the user is taken (at S12), and the integratedvalue, i.e., focusing degree F of the high-frequency componentscontained in the acquired eye image is determined (at S13). It is thedecided (at S14) whether or not the data necessary for setting thefocusing threshold have been acquired. The series operations from StepS12 to Step S14 are repeated till the data necessary for setting thefocusing threshold are acquired. The data necessary for setting thefocusing threshold at this time are focusing degree F of the plural eyeimages, which have been taken within the range of the imaging distancecontaining focal range Xw and longer than focal range Xw. Thedescription is made on the case, in which the images are consecutivelytaken by bringing the camera gradually closer from the distant position.The image taking operations are started from that of an eye image havinglow focusing degree F. The data are on focusing degrees F of the pluraleye images, in which focusing degree F becomes gradually larger andbecomes again smaller after it exhibited maximum Fmax.

Maximum Fmax is determined from the data of plural focusing degrees F,and focusing threshold Fth is set (at S15) by multiplying maximum Fmaxby the predetermined coefficient (i.e., 0.8 in this embodiment). Atlast, a message indicating the end of the threshold setting is outputtedby an image or speech (at S16). Thus, focusing threshold Fth intrinsicto the authorized user can be set for the authorized user.

By thus setting focusing threshold Fth at the optimum value intrinsic tothe authorized user, the focused eye image can be reliably acquired evenwith the small, light and inexpensive fixed focus lens.

In another method for setting focusing threshold Fth, a scale cut to thelength of the focal distance can be used at the focusing thresholdsetting time. Then, the focusing threshold can be more simply set incase the eye image can be taken with the imaging distance being fixed atfocal distance Xf for the just focus. The high-frequency componentscontained in the eye image at this time exhibit maximum Fmax. Therefore,focusing threshold Fth may be set by multiplying maximum Fmax by thecoefficient (0.8).

Of eye image taking device 100 in Embodiment 1, the operations of thefocusing decision at the iris authenticating time will be brieflydescribed in the following. It is assumed that focusing threshold Fthhas already been set.

At first, the eye image is taken to determine the high-frequencycomponents contained, i.e., focusing degree F. If this value is atfocusing threshold Fth or higher, it is decided that a focused eye imagehas been obtained, and the eye image output is outputted together withthe focus deciding output to the iris authenticating device. In casefocusing degree F is lower than focusing threshold Fth, the eye image istaken again. At this time, a message to change imaging distance X may beoutputted to the user.

EMBODIMENT 2

FIG. 4 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 2 of the invention. Blocks identical tothose of Embodiment 1 are designated by the common reference numerals.The eye image taking device of Embodiment 2 is largely different fromthe eye image taking device of Embodiment 1 in that the focus decisionis made on the basis of not focusing degree F of the eye image but irisdiameter R of the eye image. Eye image taking device 200 in Embodiment 2is provided with: imaging unit 120; iris diameter calculating unit 230for calculating the iris diameter of each eye image; reference diametersetting unit 250 for setting the reference iris diameter intrinsic tothe authorized user; and focus deciding unit 240 (as will be called the“second focus deciding unit” so that it may be discriminated from thefocus deciding unit in Embodiment 1) for deciding the focus by comparingthe iris diameter and the reference iris diameter.

Iris diameter calculating unit 230 includes pupil detecting portion 231,circumference integrating portion 232 and diameter calculating portion233. Iris detecting portion 231 binarizes the acquired eye image toextract a low luminance area, decides the pupil from the shape and sizeof the area, and determines the central coordinates of the area to setthe coordinates as the pupil center. Circumference integrating portion232 integrates the eye image circumferentially around the iris center,and diameter calculating portion 233 finds the boundary point betweenthe iris and the white portion from the circumferentially integratedvalues and outputs the boundary point as iris diameter R.

Second focus deciding unit 240 decides the focus by comparing irisdiameter R calculated from the eye image, with reference iris diameterRf, which has been determined in advance by a method, as will bedescribed hereinafter. In case the eye image to be used for theauthentication is not obtained, it is decided according to the magnituderelation between iris diameter R and reference iris diameter Rf whetherthe imaging distance is to be increased or decreased so as to acquire aneye image of a high focusing degree.

Reference diameter setting unit 250 sets reference iris diameter Rf inthe following manner for the authorized user of the mobile terminaldevice, in which eye image taking device 200 in Embodiment 2 of theinvention is installed. At first, a measure having the focusing distancedrawn therein is used to fix the distance between the eye image takingdevice and the eye at focal distance Xf or the just focus. Then, the eyeimage is taken by imaging unit 120, and iris diameter R is calculated byiris diameter calculating unit 230. Reference diameter setting unit 250sets this iris diameter R as reference iris diameter Rf.

FIG. 5 is a diagram showing relations of imaging distance X, andmagnification K of an image to be taken and iris diameter R. Here:letters Kf designate the magnification of an image at imaging distanceXf; letters Ks and Ki designate the upper limit and the lower limit ofthe magnification of the image within focal range Xw; letters Rfdesignate the iris diameter at imaging distance Xf; and letters Rs andRi designate an upper limit and a lower limit of the iris diameter infocal range Xw. Generally in the imaging unit using the fixed focuslens, magnification K is small in case imaging distance X is large, butis large in case imaging distance X is small. These relations arepredetermined by the optical system used in the imaging unit. On theother hand, iris diameter R and magnification K are proportional to eachother, and iris diameter R is not varied by the change or the like inthe environment so that the focus decision using iris diameter R can bemade by knowing iris diameter Rf in focal distance Xf.

In Embodiment 2 like Embodiment 1, it is difficult in the practical useto take the image at that distance Xf, in which the imaging distance isthe just focus. It is, therefore, practical to perform theauthentication while assuming that the eye image is focused, if thefocus is got within the iris authentication without any practicaltrouble. FIG. 5 designates such an allowable range of the iris diameterby Rw as corresponds to focal range Xw of that imaging distance.

If allowable range Rw is excessively widened, the authentication isdifficult in this case, too, because an eye image out of focus is taken.If narrowed, on the contrary, a better focused satisfactory eye image isobtained, but the focal range becomes narrower so that the focusdecision becomes harder. Thus, allowable range Rw of the iris diameteris desired to be suitably set according to the optical characteristicsof imaging unit 120, the characteristics of the iris authenticatingdevice to be connected, and the using purpose of the iris authenticatingdevice.

In eye image taking device 200 in Embodiment 2, the iris diameter iscalculated from the eye image so that the number of calculations becomeslarger than that of the calculation of the focusing degree. In case theacquired eye image does not fall in the focusing range, on the contrary,it is advantageous to know whether the iris diameter is too larger orsmaller. In this case, therefore, it is known whether or not the camerashould be brought closer or farther, so that the message to guide to aproper imaging distance can be given to the user.

As shown in FIG. 5, imaging distance X and magnification K of the imageto be taken are made to correspond one-to-one in the relation, which isdetermined by the optical system used in the imaging unit, and irisdiameter R and magnification K correspond one-to-one if limited to theauthorized user. By knowing the iris diameter in the known imagingdistance such as iris diameter Rf in focal distance Xf, therefore,imaging distance X can be calculated back from the value of irisdiameter R.

EMBODIMENT 3

FIG. 6 is a block diagram showing a configuration of an eye image takingdevice according to Embodiment 3 of the invention. The same blocks asthose of Embodiment 1 and Embodiment 2 are designated by the commonreference numerals.

Eye image taking device 300 in Embodiment 3 is provided with: imagingunit 120; focusing degree calculating unit 130; threshold setting unit150; focus deciding unit 140 (as will be called the “first focusdeciding unit”) 140; iris diameter calculating unit 230; second focusdeciding unit 241; and reference diameter setting unit 251. Thus, thecircuit blocks of eye image taking device 300 in Embodiment 3 areprovided with the circuit blocks of the eye image taking device ofEmbodiment 1 and the circuit blocks of the eye image taking device ofEmbodiment 2.

Reference diameter setting unit 251 sets reference iris diameter Rf inthe following manners for the authorized user of the mobile terminaldevice, which has eye image taking device 300 of Embodiment 3 of theinvention installed therein. At first, eye images are taken at differentimaging distances X to obtain plural eye images corresponding todifferent imaging distances X, and focusing degrees F are determined forthe individual eye images. From the plural eye images, the eye imagehaving maximum focusing degree F is determined, and its iris diameter Ris calculated so that its value is used as reference iris diameter Rf.

The reasons for thus setting the reference iris diameter Rf are that theimaging distance, at which focusing degree F takes maximum Fth, is focaldistance Xf, as has been described in Embodiment 1, and that irisdiameter R of the eye image taken at focal distance Xf can be set asreference iris diameter Rf, as has been described in Embodiment 2.

FIG. 7 is a diagram schematically showing relations between irisdiameter R and focusing degree F for different users, and letters A, Band C designate the three users shown in FIG. 2. FIG. 7 is differentfrom FIG. 2 in that the abscissa indicates not imaging distance X butiris diameter R. The reason why iris diameters Rf at the time whenfocusing degree F indicates maximum Fmax are different for theindividual users is that the iris sizes are different for the individualusers. In this example, it is indicated that user A has the largest irisand that user C has the smallest iris. FIG. 7 plots reference irisdiameter Rf, allowable range Rw (having upper limit Rs and lower limitRi) of the iris diameter, and focusing threshold Fth for user A or theauthorized user.

In this case, too, an effect to lower the authentication factor for thenon-authorized users (i.e., users B and C of FIG. 7) can be obtained, ashas been described in connection with Embodiment 1, by optimizingallowable range Rw of the iris diameter and focusing threshold Fth forauthorized user A.

Here will be described the operations of eye image taking device 300 ofEmbodiment 3 for the focus decisions at the iris authenticating time. Itis assumed that focusing threshold Fth and reference iris diameter Rfhave already been set. FIG. 8 is a flow chart showing an eye imagetaking procedure of the eye image taking device in Embodiment 3 of theinvention at the iris authenticating time.

First of all, the eye image of the user is taken (at S31) to determinefocusing degree F of the acquired eye image (at S32). This focusingdegree F is compared with focusing threshold Fth to decide (at S33)whether or not the acquired eye image is such an focused image as can beauthenticated on the iris. In case focusing degree F is focusingthreshold Fth or higher, an authenticatable eye image can be acquired.Therefore, the eye image signals are outputted together with the focusdecision result to the iris authenticating device (at S34). In casefocusing degree F is lower than focusing threshold Fth, iris diameter Rof the acquired eye image is determined (at S35) and is compared withreference iris diameter Rf (at S36). In case iris diameter R is smallerthan reference iris diameter Rf, a message to bring the camera closer tothe eye is outputted (at S37), and the procedure returns to Step S31. Incase iris diameter R is larger than reference iris diameter Rf, on theother hand, a message to bring the camera apart from the eye isoutputted (at S38), and the procedure returns to Step S31.

By thus using the small, light and inexpensive fixed focus lens, it ispossible to take the eye image, which makes the iris authenticationpossible.

In the flow chart shown in FIG. 8, the procedure always advances to StepS35, in case focusing degree F does not satisfy focusing threshold Fthat Step S33. However, the procedure to advance from Step S33 to Step S35may be only once for several times and may otherwise advance from StepS33 to Step S31.

The following advantages are attained from eye image taking device 300of Embodiment 3, which is provided with the two decision units of firstfocus deciding unit 140 and second focus deciding unit 241. Thecalculations of focusing degree F necessary for deciding first focusdeciding unit 140 can be executed by the relatively simple ones toextract and integrate the high-frequency components. Therefore, the timeperiod for the calculations can be shortened so that the calculations onthe image signals inputted can be performed in real time. In case,however, the imaging distance of the eye image fails to fall within thefocused range, whether or not the camera is brought closer cannot beknown from the value of focusing degree F. On the other hand, thecalculations of iris diameter R necessary for the decision of secondfocus deciding unit 241 are made at first by determining the iris centerfrom the eye images and then by performing the circumferentialintegration thereby to identify the iris diameter. Thus, the time periodfor the calculations is elongated. On the contrary, the imaging distancecan be estimated to inform which way the camera is to be moved in orderto obtain the focused eye image. Therefore, the focus decision is madeby first focus deciding unit 140 of the shorter calculation time. Incase the focus decision cannot be obtained, the decision of second focusdeciding unit 241 is made to inform the user in which way the camera isto be moved. It is possible to attain the eye image, which is focusedfor a short time.

In the description thus far made, the eye image for highest focusingdegree F is derived from the plural eye images of different imagingdistances, and its iris diameter R is used as reference iris diameterRf. However, focusing threshold Fth, and upper limit Rs and lower limitRi of the allowable range of the iris diameter may be determined in thefollowing manners.

When the authorized user registers the iris information, the eye imageis taken at first by varying the distance of the eye image taking devicefrom the eye, to calculate focusing degrees F and iris diameters R,which are contained in the individual eye images. Next, an approximatefunction F=F(R) indicating the relation between focusing degrees F andiris diameters R, which are determined from the plural eye images. Fromsets of two iris diameters R1 and R2 of equal focusing degrees i.e.F(R1)=F(R2), moreover, there is selected the set, in which the ratio ofR2/R1 of the iris diameters is equal to the ratio of Ki/Ks of the imagemagnifications. Values R1 and R2 of the iris diameters are set to upperlimit Rs and lower limit Ri of the allowable range of the irisdiameters, and focusing degree F at this time is set to focusingthreshold Fth.

Here, the relation between focusing degree F and iris diameter R neednot to be functionally approximated. However, the data of focusingdegrees F and iris diameters R, which are obtained from the plural eyeimages, are discrete. If that relation is approximated by the continuousfunction, therefore, the calculations can be made easy, and the data canbe interpolated. Thus, the advantage obtained is that focusing thresholdFth, and allowable range Rs and Ri of the iris diameter can be moreprecisely set.

If the allowable range of the iris diameter and focusing threshold Fththus set are used, an advantage is that the decision results of thefirst focus deciding unit and the second focus deciding unit aresubstantially identical.

According to the invention, it is possible to provide the eye imagetaking device, which can make a stable focus decision irrespective ofthe shape of the eye of the user by using the small, light andinexpensive fixed focus lens and which can be installed in the mobileterminal device.

INDUSTRIAL APPLICABILITY

The eye image taking device of the invention can make a stable focusdecision irrespective of the shape of the eye of the user by using thesmall, light and inexpensive fixed focus lens and can be installed inthe mobile terminal device. Thus, the invention is useful in an eyeimage taking device, especially in the eye image taking device which canbe installed in the mobile terminal device.

1. An eye image taking device comprising: an imaging unit for taking aneye image of a user; a focusing degree calculating unit for calculatinga focusing degree from the eye image taken at the imaging unit; athreshold setting unit for setting a focusing threshold intrinsic to anauthorized user; and a focus deciding unit for deciding a focus bycomparing the focusing degree and the focusing threshold, wherein thethreshold setting unit sets the focusing threshold on the basis of theeye image of the authorized user.
 2. An eye image taking deviceaccording to claim 1, wherein the focusing degree calculating unitcalculates the magnitude of the high-frequency components contained inthe eye image taken by the imaging unit, as the focusing degree, andwherein the threshold setting unit selects the maximum from a pluralityof focusing degrees, which are calculated individually from the pluraleye images of different imaging distances for the authorized user,thereby to set the focusing threshold on the basis of the maximum.
 3. Aneye image taking device according to claim 1, wherein the thresholdsetting unit sets the focusing threshold on the basis of the focusingdegree which is calculated from the eye images taken at the focaldistance for the authorized user.
 4. An eye image taking devicecomprising: an imaging unit for taking an eye image of a user; an irisdiameter calculating unit for calculating an iris diameter in the eyeimage; a reference diameter setting unit for setting a reference irisdiameter intrinsic to an authorized user; and a focus deciding unit fordeciding a focus by comparing the iris diameter and the reference irisdiameter, wherein the reference diameter setting unit sets the referenceiris diameter on the basis of the eye image of the authorized user. 5.An eye image taking device according to claim 4, wherein the referencediameter setting unit sets the value of the iris diameter, which iscalculated from the eye images taken at the focal distance for theauthorized user, as the reference iris diameter.
 6. An eye image takingdevice comprising: an imaging unit for taking an eye image of a user; afocusing degree calculating unit for calculating a focusing degree fromthe eye image taken at the imaging unit; a threshold setting unit forsetting a focusing threshold intrinsic to an authorized user; a firstfocus deciding unit for deciding a focus by comparing the focusingdegree and the focusing threshold; an iris diameter calculating unit forcalculating an iris diameter in the eye image; a reference diametersetting unit for setting a reference iris diameter intrinsic to theauthorized user; and a second focus deciding unit for deciding a focusby comparing the iris diameter and the reference iris diameter, whereinthe focus decision is made at the second focus deciding unit in case thedecision of the focus cannot be obtained at the first focus decidingunit.
 7. An eye image taking device according to claim 6, wherein thereference diameter setting unit sets the iris diameter in the eye imageof the maximum focusing degree of the plural eye images of differentimaging distances, as the reference iris diameter for the authorizeduser.
 8. An eye image taking device according to claim 6, wherein thereference diameter setting unit sets the values of such two of theplural iris diameters calculated individually from the plural eye imagesof different imaging distances as have an equal focusing degree and aniris diameter ratio equal to a predetermined value, as two referenceiris diameters for the authorized user, and wherein the thresholdsetting unit sets the focusing degree as the focusing threshold.